He left because he decided to pick revenge over everything else, he decided he was going to use Orochimaru to get strong enough to kill his brother. None of it is really whiny at all imo. He choose his path, and stuck with. He threw everything away for the chance to complete his goal. And yet, he still refused to kill other people. Then he finally achieved his objective, and learns his whole life was a lie. He knew nothing. His chooses to stay on the path of revenge and sets a new goal- kill Danzo and the elders. Perfectly reasonable imo.
THEN he decides that all of Konoha should burn, and that everyone is guilty because they were living peacefully there. That is the turning point between someone driven by revenge, and someone who just kills indiscriminately. That is when I decided that he's a whiny bitch who's just mad.
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